Communication systems designed to allow multiple users to access a common communications medium may be based on code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), space division multiple access (SDMA), polarization division multiple access (PDMA), or other modulation techniques known in the art. These modulation techniques demodulate signals received from multiple users of a communication system, thereby enabling an increase in the capacity of the communication system. In connection therewith, various wireless systems have been established including, e.g., Advanced Mobile Phone Service (AMPS), Global System for Mobile communication (GSM), and some other wireless systems.
In conventional wireless communications, an access network is generally employed to support communications for a number of devices. An access network is typically implemented with multiple fixed site base stations dispersed throughout a geographic region. The geographic region is generally subdivided into smaller regions known as cells. Each base station may be configured to serve the devices in its respective cell. An access network may not be easily reconfigured when there are varying traffic demands across different cellular regions.
In contrast to the conventional access network, ad-hoc networks are dynamic. An ad-hoc network may be formed when a number of wireless communication devices, often referred to as terminals, join together to form a network. Terminals in ad-hoc networks can operate as either a host or router. Thus, an ad-hoc network may be easily reconfigured to meet existing traffic demands in a more efficient fashion. Moreover, ad-hoc networks do not require the infrastructure required by conventional access networks, making ad-hoc networks an attractive choice for the future.
In a conventional CDMA communications system, a subscriber station may access a network, or communicate with other subscriber stations, through one or more base stations. A subscriber station can also be called a terminal. Each base station is configured to serve all subscriber stations in a specific geographic region generally referred to as a cell. In some high traffic applications, the cell may be divided into sectors with a base station serving each sector. Each base station transmits a pilot signal which is used by the subscriber stations for synchronizing with a base station and to provide coherent demodulation of the transmitted signal once the subscriber station is synchronized to the base station. The subscriber station generally establishes a communications channel with the base station having the strongest pilot signal.
The subscriber station calculates a signal-to-noise-and-interference ratio C/I for a received forward link signal. The forward link refers to transmission from the base station to a subscriber station and the reverse link refers to transmission from the subscriber station to a base station. The subscriber station's C/I determine the data rate that can be supported for the forward link from the base station to a subscriber station. That is, a given level of performance for the forward link is achieved at a corresponding level of C/I. A method and apparatus for selecting a data rate is disclosed in U.S. Pat. No. 6,574,211 entitled “METHOD AND APPARATUS FOR HIGH RATE PACKET TRANSMISSION,” issued Jun. 3, 2003, which is assigned to the assignee of the present invention.
The power at which a base station transmits data to a subscriber station is called the forward link transmit power. The forward link transmit power is at a level required for transmitting data over the forward link reliably. Likewise, the power at which a subscriber station transmits data to a base station is called the reverse link transmit power. The reverse link transmit power is at a level required for transmitting data over the reverse link reliably.
Interference to each subscriber station increases as the number of subscriber stations transmitting increases. Thus, it is desirable to control subscriber station transmit power to avoid adverse interference with other subscriber station communications.
Ultra-Wideband (UWB) is an example of a communications technology that may be implemented with ad-hoc networks. UWB provides high speed communications over a wide frequency bandwidth. At the same time, UWB signals are transmitted in very short pulses that consume very little power. The output power of the UWB signal is so low that it looks like noise to other RF technologies, making it less interfering.
In an ad-hoc network, terminals are added dynamically. As more terminals are added, each communicating terminal creates more interference for terminals other than the terminal with which it is communicating. Thus, it is desirable to control terminal transmit power to avoid adverse interference with other terminal communications.
A wireless communication system, whether convention or ad-hoc, that utilizes a rake receiver, diversity combines separable multipaths. In a rake receiver, a demodulation element, or “finger” is assigned to a multipath. When receive power consumption is dominated by the power consumption in the rake fingers, a system and method that reduces rake finger processing also significantly reduces power consumption.
Thus, what is needed is a system and method to reduce rake finger processing to reduce power consumption in the communication system.